1. Field of the Invention
The present invention relates to an electric heater, particularly as an auxiliary heating means for an automotive vehicle.
2. Description of the Related Art
For use in automotive vehicles, particularly automotive vehicles with new, consumption-optimized engines, in which a reduced amount of heat energy is observed, electric auxiliary heaters are used for heating passenger compartment and engine. Such electric heaters are however also suited for other purposes, e.g. in the field of building installations, particularly air conditioning, in industrial plants, or the like.
Preferably, PTC heating elements with radiator elements in heat-conducting communication are used for such an electric auxiliary heater for an automotive vehicle. The heat generated by the PTC heating elements is discharged via the radiator elements to the air flowing therethrough. The total assembly consisting of a layered structure of PTC heating elements, radiator elements and contact sheets, which serve the supply of power, is kept in a clamp fit within a frame for increasing the efficiency of the heater. Due to clamping action a high electrical and thermal contacting of the PTC heating elements is achieved.
The layered structure is held within a stable frame having a preferably U-shaped cross-section. The frame is configured such that it compresses the layered structure. The clamping action can alternatively be effected by resilient elements arranged within the layered structure. To enable the frame to absorb the resilient forces, it is made particularly stable from a mechanical point of view. Preferably, it is configured with a U-shaped cross-section. Such a conventional heater is e.g. known from DE-A-101 21 568.
The minimum height of the longitudinal bars of such a frame with U-shaped cross-section (or C-shaped cross-section according to DE-A-101 21 568) is about 11 mm with respect to the necessary clamping forces. This gives the whole heater a height of at least 22 mm that cannot be used for the passage of air. Such a constructional shape with exterior clamping action or exterior holding frame has therefore a large area that cannot be used for air throughput. That is why such electric heaters are not suited for use in the case of very small installation heights.
When electric heaters with an exterior holding frame or exterior clamping action are assembled, troublesome measures are needed for counteracting the contact pressure forces of the resilient means/frame that are objectionable during assembly.
Due to these drawbacks heaters with a conventional holding frame for modern air conditioners, especially for installation in automotive vehicles, are less and less suited. Air conditioners for multi-zone air conditioning in a comfort-based automotive vehicle require more and more heaters of a large length, but small constructional height.
Furthermore, conventional constructions with a holding frame, particularly of metal, have a considerable weight. However, it is desired for installation into automotive vehicles with respect to the total weight of the vehicle that electric auxiliary heaters should be used with a particularly low weight.
A further drawback of metal holder frames is their conductive surface. To enhance the safety in automotive vehicles, metal surfaces are more and more avoided so that their contact is possible without any risk, i.e. without electrical or thermal conduction. To this end the above-described heaters are preferably provided with a coating of plastics, as is e.g. the case with the heater shown in DE-A-101 21 568.